The present invention is directed to a thermal timer and, more particularly, to a timer device that produces a distinguishable output at a time determined by a thermal dissipation or thermal leakage parameter.
Moreover, the present invention is directed to a thermal timer device for effecting a warning signal function on a range appliance or the like during operation and subsequent cool down to a temperature that is relatively safe to the touch of at least a portion of such a range or the like. It will be appreciated, however, that the thermal timer of the invention may be otherwise used to effect a distinguishable output for a period of time, for example, during and/or after the thermal energy supply thereto has been terminated.
A signal pilot light has been used to indicate to an operator of a range that has a smooth or imperforate top, which shields the electric or gas heating element or elements, that a heating element beneath the top is energized. The heat energy transferred through the top then may be used for the usual purpose of cooking food in a utensil placed on the top, and in the course of such operation the top becomes hot to the point of being unsafe to the operator's touch. While the heating element is energized, the usually also energized signal pilot light provides a suitable signal thereof. However, after the heating element which may be, for example, an electric resistance-type, a gas burner-type, or other suitable type that ultimately may be employed to effect heating of food, a cooking utensil or the like placed on the cook top, has been de-energized, for example, by turning off the electric energy or gas supply thereto, the previously heated area of the cook top will remain relatively hot for a period of time, although the signal pilot light will have been extinguished upon such de-energization of the heating element. The time required for the hot area of the cook top to cool down to near ambient temperature varies with cook top-ambient temperature differential, the material of the cook top and its thermal capacity, and it has been found that many conventional solid cook tops will cool down to near ambient temperature after having been heated to maximum normal operating temperature in approximately 30 to 40 minutes after the heating element has been de-energized.
Accordingly, there is a need to give a warning signal to the range operator or other person that an area of the cook top is hot and unsafe to touch while that area cools down after the heating element therebeneath has been de-energized. Since conventional thermostats do not have an operational temperature range, say, for example, between a safe near ambient temperature of 140.degree. F. and approximately 1,500.degree. F., the temperature often reached by the heating element of a range, it is not possible to use a warning light operated by a simple thermostat positioned in proximity to a heating element to monitor the cook top temperature. Therefore, it has been proposed to use a timer device triggered to operate a warning light for a period of time when the heating element has been de-energized. While conventional electrical timer devices may be used to operate such a warning light, these timer devices may be relatively expensive and/or unable to withstand the normal temperatures and other environmental conditions present in a range, etc., and for these and other reasons are undesirable.